Exploring the Global Importance of Atmospheric Ammonia Oxidation
Name
CalNexSOAS_draft_vpostReReview.pdf
Description
Accepted version
Size
1.07 MB
Format
Adobe PDF
Checksum (MD5)
b199da3534d2554f33f83e1b68a8231c
Author(s)
Pai, Sidhant J
Heald, Colette L
Murphy, Jennifer G
Date Issued
2021
Journal
ACS Earth and Space Chemistry
Publisher
American Chemical Society (ACS)
Citation
Pai, Sidhant J, Heald, Colette L and Murphy, Jennifer G. 2021. "Exploring the Global Importance of Atmospheric Ammonia Oxidation." ACS Earth and Space Chemistry, 5 (7).
Version
Author's final manuscript
Abstract
Ammonia (NH3) is the dominant source of reduced nitrogen in the atmosphere, emitted primarily from agricultural activities. Current representations of NH3 in global chemical transport models (CTMs) largely focus on the thermodynamics governing aerosol formation, ignoring the atmospheric oxidation of NH3 with the hydroxyl (OH) radical since this process is slow and therefore assumed to not be significant. In this study, we incorporate an explicit mechanism to simulate this chemistry using the GEOS-Chem global CTM. While the inclusion of this pathway does not result in a meaningful impact on the global ammonia burden, with an average annual reduction of approximately 3%, the oxidation process leads to small but significant changes in key atmospheric species, particularly over the Indian subcontinent where surface concentrations of ozone (O3), OH, and nitrate aerosol see reductions of over 5%. Our results also suggest that ammonia oxidation accounts for around 8% (and up to 16%) of the global anthropogenic nitrous oxide (N2O) source, with important implications for climate models designed to accurately simulate the impact of changing agricultural emissions. We also conduct a suite of simulations using anthropogenic emission estimates from the representative concentration pathway (RCP) trajectories for 2100, which suggest that the atmospheric oxidation of NH3 will become an increasingly important source of N2O and NOx under future emission scenarios, accounting for up to 21% of future N2O emissions. Given the large uncertainties in the oxidation process, we use a sensitivity analysis to demonstrate the wide range in atmospheric response; our results support the need for further research to better constrain the reaction pathways and associated yields.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
Terms of Use
Creative Commons Attribution-Noncommercial-Share Alike
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1021/ACSEARTHSPACECHEM.1C00021
